Readsorption

Readsorption is the process by which species that have been desorbed from a solid surface subsequently reattach to the same surface or to another surface within the same system. It is a common phenomenon in adsorption–desorption processes involving porous or heterogeneous materials, such as activated carbon, silica, zeolites, soils, or catalyst supports. Readsorption can occur in gas-phase or liquid-phase experiments and may take place immediately after desorption or after diffusion within interconnected pores.

Mechanisms include rapid reattachment to adjacent adsorption sites, diffusion of desorbed molecules into pores where they encounter additional sorption sites, and, in some cases, structural changes that expose new binding sites. Readsorption can involve single-layer or multi-layer adsorption if desorbed molecules encounter other adsorbed species before leaving the surface.

Consequences: Readsorption can slow apparent desorption rates, distort desorption isotherms and kinetic analyses, and contribute to tailing or hysteresis in adsorption–desorption cycles. It can lead to underestimation of desorption efficiency if not accounted for and complicates the interpretation of retention in environmental and industrial processes.

Applications and relevance: In environmental science, readsorption affects contaminant mobility in soils and porous media. In separations and chromatography, it can cause tailing peaks and reduced recovery. In catalysis and energy storage, readsorption of reactive intermediates or adsorbed species can influence reaction cycles and device performance. Researchers model readsorption using multi-site or time-dependent kinetic frameworks and take steps to minimize it during measurement, such as controlled purge conditions or post-desorption regeneration.

The term is used to describe reattachment events that occur after desorption during continued exposure or in subsequent cycles.